(1) Field of the Invention
The present invention relates to a flight velocity vector measuring system in a wide velocity region using a truncated-shape probe, and more particularly to a flight velocity measuring system in a wide velocity region using a square truncated pyramid-shape probe capable of measuring a flight velocity vector by a calculation process on the basis of air data obtained by the square truncated pyramid-shape probe in a wide velocity region from a low velocity to a supersonic velocity.
(2) Description of the Related Art
A flight velocity vector measuring system for measuring a flight velocity vector using a square truncated pyramid-shape probe so far known has been proposed by the present inventors (see U.S. Pat. No. 5,423,209 specification). In the conventional flight velocity vector measuring system using a square truncated pyramid-shape probe, the probe is mainly directed at the low speed region which is not affected by compressibility and shock wave. The calculation of the flight velocity vector is done on the basis of dynamic pressure. The flight velocity vector is computed by substituting five pressure information (that is, a total pressure and four pressures on a truncated pyramid-shape surface) obtained from the square truncated pyramid-shape probe and pressure calibration coefficients obtained in advance into a polynomial approximation and using a Newton-Raphson method (a repetition computing method). Further, the pressure calibration coefficients are calculated on the basis of the dynamic pressure in the flight change and five pressure information every change of probe angle.
In general, for definition of velocity representative of the magnitude of velocity in a region from low velocity to supersonic velocity, Mach number is applied taking a concept of sonic velocity into consideration. Since the air current is changed into an incompressible flow, a compressible flow and a flow caused by a shock wave according to the velocity region, the Mach number is obtained by separate operational expressions corresponding to these flows. That is, in the low velocity flight, the velocity is simply obtained from the dynamic pressure obtained by a difference between total pressure and static pressure without taking the compressibility into consideration. Further, since the compressibility influences on the probe as the velocity comes close to the sonic velocity, the velocity should be obtained by an expression which takes the compressibility into consideration. Furthermore, in the case of the flight beyond the sonic velocity, the shock wave is generated in front of the probe so that the pressure information detected before and behind the shock wave. Therefore, the velocity is obtained by using an operational expressing which takes these into consideration. In the case of flight at a large attitude angle in velocity regions, it is important to take an influence of all pressure differentials caused by a movement of a stagnation point of the probe into consideration.
From the above-described fact, in the case of flight at a high attitude angle in a wide velocity region, in the flight velocity vector calculation process according to a set of pressure calibration coefficients, it is difficult to enhance the measuring accuracy. Further, when the probe calibration coefficient every velocity is used in order to secure the accuracy, the process time increases, making it difficult to put to practical use.